A four-roller tube-making machine is known having a pair of axially spaced end supports in which are journaled the ends of upper and lower large-diameter bending rollers. Normally the ends of the lower rollers are limitedly axially displaceable in the end supports. Furthermore a pair of small-diameter side rollers horizontally flank the upper and lower rollers and have ends journaled and limitedly displaceable in the end supports. Such an arrangement is used for bending or crimping plate stock, and can be employed for smoothing a large-diameter pipe formed by closing and welding the crimped plate stock.
It is known from German Pat. No. 428,482 to provide so-called support rollers for the lower roller. These support rollers can bear upwardly on the lower bending roller and can normally be moved along an axially extending track or rail of the machine.
German Pat. No. 960,090 has upper support rollers downwardly effective on the upper bending roller, and mounted on an axially extending traverse or rail whose ends are releasably mounted on the end supports. This traverse is in the way during smoothing of a tube, during which operation the radial forces effective on the bending rollers are considerably less than during bending or crimping. Thus it is necessary to use a different machine to round or smooth a closed and welded tube.
As the known systems of supporting the bending rollers other than at their ends cannot be employed in many applications, it is possible to substantially overdimension the machine so that even without such intermediate support it is possible for the rollers to exert the necessary forces on the workpiece during crimping or bending. Such overdimensioning obviously leads to increased equipment costs and operating expenses.